<template>
  <div class="upload-excel">
    <!-- 按钮盒子 -->
    <div class="btn-upload">
      <el-button :loading="loading" size="mini" type="primary" @click="handleUpload"> 点击上传 </el-button>
    </div>

    <!-- 隐藏的 file 框 -->
    <input ref="excel-upload-input" class="excel-upload-input" type="file" accept=".xlsx, .xls" @change="handleClick">

    <!-- 拖拽盒子 -->
    <div class="drop" @drop="handleDrop" @dragover="handleDragover" @dragenter="handleDragover">
      <i class="el-icon-upload" />
      <span>将文件拖到此处</span>
    </div>
  </div>
</template>

<script>
import XLSX from 'xlsx'

export default {
  name: 'UploadExcel',
  props: {
    beforeUpload: Function, // eslint-disable-line
    onSuccess: Function// eslint-disable-line
  },
  data() {
    return {
      loading: false,
      excelData: {
        header: null,
        results: null
      }
    }
  },
  methods: {
    generateData({ header, results }) {
      this.excelData.header = header
      this.excelData.results = results
      // 调用 this.onSuccess，把解析好之后的结果传递过去
      this.onSuccess && this.onSuccess(this.excelData)
    },
    handleDrop(e) {
      e.stopPropagation()
      e.preventDefault()
      if (this.loading) return
      // !拿到拖拽过来的文件信息
      const files = e.dataTransfer.files
      // !只能拖过来一个文件
      if (files.length !== 1) {
        this.$message.error('Only support uploading one file!')
        return
      }
      // !拿到拖过来的文件
      const rawFile = files[0] // only use files[0]

      // !判断传递过来的是否是一个 excel 文件，不是就返回
      if (!this.isExcel(rawFile)) {
        this.$message.error('Only supports upload .xlsx, .xls, .csv suffix files')
        return false
      }
      this.upload(rawFile)
      e.stopPropagation()
      e.preventDefault()
    },
    handleDragover(e) {
      e.stopPropagation()
      e.preventDefault()
      e.dataTransfer.dropEffect = 'copy'
    },
    handleUpload() {
      this.$refs['excel-upload-input'].click()
    },
    handleClick(e) {
      const files = e.target.files
      const rawFile = files[0] // only use files[0]
      if (!rawFile) return
      this.upload(rawFile)
    },
    upload(rawFile) {
      // !保证即便两次上传同一个文件，也能触发 input:file 的 change 事件
      this.$refs['excel-upload-input'].value = null // fix can't select the same excel

      // 如果外界没有传递 beforeUpload
      if (!this.beforeUpload) {
        // 直接读取文件
        this.readerData(rawFile)
        return
      }
      // !传递了 beforeUpload，直接调用的同时并把文件信息传递过去
      const before = this.beforeUpload(rawFile)
      // !只有 beforeUpload 返回的是 true，才走后续的逻辑
      if (before) {
        this.readerData(rawFile)
      }
    },
    readerData(rawFile) {
      this.loading = true
      return new Promise((resolve, reject) => {
        // 创建一个读取文件信息的一个对象
        const reader = new FileReader()
        reader.onload = e => {
          // 监听 onload 拿到读取到的结果
          // e.target.result 就是二进制的结果
          const data = e.target.result
          // !xlsx 这个包把读取到的文件信息解析成 JS 中能使用的普通的数据
          const workbook = XLSX.read(data, { type: 'array' })
          const firstSheetName = workbook.SheetNames[0]
          const worksheet = workbook.Sheets[firstSheetName]
          const header = this.getHeaderRow(worksheet)
          const results = XLSX.utils.sheet_to_json(worksheet)
          // !header 和 results 就是解析好之后的结果
          this.generateData({ header, results })
          this.loading = false
          resolve()
        }
        // 读取文件信息为 ArrayBuffer（二进制），读取的操作是异步的
        // 需要在 onload 里面拿到读取到的结果
        reader.readAsArrayBuffer(rawFile)
      })
    },
    getHeaderRow(sheet) {
      const headers = []
      const range = XLSX.utils.decode_range(sheet['!ref'])
      let C
      const R = range.s.r
      /* start in the first row */
      for (C = range.s.c; C <= range.e.c; ++C) { /* walk every column in the range */
        const cell = sheet[XLSX.utils.encode_cell({ c: C, r: R })]
        /* find the cell in the first row */
        let hdr = 'UNKNOWN ' + C // <-- replace with your desired default
        if (cell && cell.t) hdr = XLSX.utils.format_cell(cell)
        headers.push(hdr)
      }
      return headers
    },
    isExcel(file) {
      return /\.(xlsx|xls|csv)$/.test(file.name)
    }
  }
}
</script>

<style scoped lang="scss">
    /* 全部覆盖 */
    .upload-excel {
        display: flex;
        justify-content: center;
        margin-top: 100px;

        .excel-upload-input {
            display: none;
            z-index: -9999;
        }

        .btn-upload,
        .drop {
            border: 1px dashed #bbb;
            width: 350px;
            height: 160px;
            text-align: center;
            line-height: 160px;
        }

        .drop {
            padding-top: 20px;
            line-height: 80px;
            color: #bbb;

            i {
                font-size: 60px;
                display: block;
            }
        }
    }
</style>
